Estimation Of Crack Propagation Research Articles

Fretting fatigue behavior of metal injection molded stainless steel MIM 316L with small pores and low porosity

The fretting fatigue of metal injection molded stainless steel (MIM 316L) with a mean pore diameter of 3 μm and porosity of 5.1% was investigated both experimentally and numerically. The granular-like wear debris accumulated in pores on the fretted surface of the MIM 316L specimen was the cause of the reduction in the tangential force coefficient, potentially improving fretting fatigue strength. These pores did not significantly influence the location of fretting crack nucleation and crack path due to high stress concentration at the fretting contact edge. Under the large-scale yielding at the crack tip and fretting-contact-induced crack opening/closure, a continuum body finite element model can be applied to estimate crack nucleation and propagation behavior, as well as fretting fatigue life.

Using video detection of snow surface movements to estimate weak layer crack propagation speeds

Abstract Dry-snow slab avalanches release due to crack propagation in a weak snow layer under a cohesive snow slab. Crack propagation speeds can provide insights into the potential size of avalanches and inform fracture and avalanche release models. Despite their importance, slope-scale crack speed measurements from real avalanches are limited. Further, most existing slope-scale measurements utilize the appearance of slab fractures on the snow surface. However, we have no evidence that the appearance of surface cracking is a good indicator of the weak layer crack propagation tip. Here we present a novel method to estimate crack propagation speed from snow surface movements in avalanche videos. Our technique uses changes in frame pixel intensity, allowing us to detect the location of weak layer cracks well before slab fractures appear on the snow surface. We use field experiments and numerical simulations to validate our method before applying it to five avalanches. Our estimates show that cracks propagate faster up and down the slope than in the cross-slope direction; this suggests that different propagation regimes likely govern crack propagation up/down the slope, cross-slope and in flat terrain.

MODELLING OF TENSILE STRAIN DISTRIBUTION ALONG THE AXIAL DIRECTION ON SIMPLIFIED DAMAGE ESTIMATION OF REINFORCED CONCRETE STRUCTURES

In recent years, studies on crack propagation analysis and evaluation methods for RC structural members have been carried out for the sake of reparability performance. The purpose of this study is to develop a simple method for estimating crack propagation without using advanced and complicated analytical techniques. This paper is divided into two main chapters: The first focuses on the relationship between axial strain distribution and crack length obtained from an experimental result to improve the existing damage estimation method. The second is a study of the applicability of the proposed theory to structural damage estimation by combining it with static incremental analysis.

Simulation of ductile fracture propagation using the elastoplastic phase-field damage method calibrated by ultrasonic wave velocity measurement

The phase-field damage theory has become a powerful approach to estimate crack propagation via the finite element method (FEM). The sharp crack is smeared into a diffusive fracture propagation zone within a length scale parameter (ℓ). However, the calibration of the phase-field damage model is still difficult, especially for the length scale parameter, which is difficult to directly observe and accurately measure in laboratory testing. In most numerical studies, the length scale parameter is arbitrarily determined as the minimum element size in FEM. However, the selection of the length scale parameter may largely affect the accuracy of the phase-field model. Also, most current phase-field models only consider elasticity and few studies further consider the ductile (plastic) fracture propagation, since the plastic recoverable energy does not have a convincing form. In this study, we aim to calibrate the elastoplastic phase-field damage model based on the traditional continuum damage mechanics, with the assistance of ultrasonic wave velocity measurement. The traditional damage variable can be back-calculated from the drop of P wave velocity, following the energy equivalence hypothesis. This traditional damage variable is shown to be consistent with the phase-field damage variable as calculated in our proposed elastoplastic phase-field damage model. Therefore, the length scale parameter can be determined from fitting the rock damage evolution. The plastic flow and its corresponding plastic-free energy are considered, using a phenomenological function obeying preliminary thermodynamic assumptions. The proposed model shows good consistency with laboratory observations. Numerical implementation of the proposed model was achieved by inserting it into COMSOL Multiphysics using a weak form formulation. This paper introduces a pragmatic approach to calibrate the phase-field damage model based on laboratory testing results.

Crack propagation in articular cartilage under cyclic loading using cohesive finite element modeling

Severe joint injuries often involve cartilage defects that propagate after mechanical loading. The propagation of these lesions may contribute to the development of post-traumatic osteoarthritis (PTOA). However, the mechanisms behind their propagation remain unknown. Currently, no numerical predictive methods exist for estimating crack propagation in cartilage under cyclic loading, yet they would provide essential insights into crack growth in injured tissue after trauma. Here, we present a numerical approach to estimate crack propagation in articular cartilage under cyclic loading using a cohesive damage model. Four different material models for cartilage (hyperelastic, poro-hyperelastic, poro-hyper-viscoelastic, and fibril-reinforced poro-hyperelastic (FRPHE) with different collagen orientations) were implemented. Our numerical cohesive damage model was able to replicate the experimental crack length reported in the literature, showing greater crack length with an increasing number of loading cycles. Damage initiation stress (4.35–4.73 MPa) and fracture energy (0.97–1.55 N/mm) values obtained for the poro-hyperelastic, poro-hyper-viscoelastic, and parallel-FRPHE models were within the range of what has been reported previously. The crack growth predictions obtained by the FRPHE models showed the influence of anisotropy of the fibrillar matrix on the cartilage response. Our results indicate that our cohesive damage model could potentially be used to estimate the adverse conditions in injured soft tissue such as osteochondral lesions, menisci tears, or partial ligament ruptures under (ab)normal biomechanical scenarios.

Lattice modeling and testing of aerated autoclaved concrete infilled frames

Significant infill wall damage in reinforced concrete frame buildings was observed in the past earthquakes. A vast number of numerical approaches have been proposed to estimate the non-linear behavior of infilled frames at different scales. Mesoscale lattice models were successfully used in the past to simulate the behavior of reinforced concrete member response. In this study, two-dimensional mesoscale lattice approach with an extended calibration technique was consistently applied to simulate the response of unreinforced Aerated Autoclaved Concrete (AAC) masonry infilled reinforced concrete frames. Two AAC infilled walls were tested for the purposes of this study. The objective of the tests were to investigate the effect of infilled wall-frame interaction with and without openings and validate the proposed numerical approach. In addition to the tests conducted, two tests were used from the literature for further validation. The maximum error of load capacity estimation from the simulations was less than 15% for all the examined tests. The proposed lattice model was capable of estimating crack propagation in the infill walls with reasonable accuracy. The frame-infill wall interaction was successfully simulated with providing a realistic representation of strut formation. Finally, a parametric study was conducted to examine contact length and strut width as a function of lateral deformation. The results show that the infill wall-frame contact length is significantly dependent on the lateral deformation demand levels and properties of interaction region.

Characteristics of cracks formed at the surface of NiTi during a single cycle of pseudoelastic deformation

Pseudoelastic deformation of NiTi usually results in cracks at the surface. Cracking is promoted by surface oxide layers that form, e.g., during heat treatments required for shape-setting of minimally invasive implants. In connection with the advancing miniaturization of minimally invasive implants, the question arises whether their mechanical integrity may get impaired by such cracks. In the present work, the characteristics of the cracks was investigated in cross section with the help of targeted preparation using focused ion-beams. SEM and TEM on samples after a single cycle of pseudoelastic deformation revealed that cracks extend perpendicular to the loading direction in the surface oxide layer and change to angles between 90° and 45° in the Ni-rich layer below. Pores observed in the surface oxide close to the Ni-rich layer did not prevent the extension of cracks towards the NiTi bulk. When the cracks reach the NiTi, blunting of the crack tip was observed. The crack length essentially corresponds to the thickness of the surface oxide layer and the Ni-rich layer. The findings provide data for estimating crack propagation in according implants in the future.

Investigation of the Crack Propagation Behavior of the Multiwalled Carbon Nanotube/Graphite/Natural Rubber Hybrid Nanocomposites Using Digital Image Correlation Technique

In the presented study, a hybrid Natural Rubber (NR) based semiconductive nanocomposites was examined to obtain better electrical and mechanical properties. The hybrid nanocomposite produced by incorporation of the Multiwalled Carbon Nanotube (MWCNT) and graphite nanoparticles into the NR. The conventional curing additives also included in the compound. A functionalized MWCNT (1, 2 and 3 phr's) with 3 phr graphite quotas were studied to produce the NR nanocomposites. The MWCNT/Graphite and NR mixed homogeneously to advance the interfacial interaction with the matrix. The graphite nano-particulates added to obtain 3D electrical connectivity network in the hybrid nanocomposites by becoming bridging points between multiwalled carbon nanotubes. Nanocomposites were produced as 3 mm sheets in a steel mold by vulcanizing at 165 °C for 10 min under pressure. The single-edge notched tension specimens were subjected to estimate crack propagation and electrical resistance relation. Digital Image Correlation (DIC) technique was used to observe the crack resistivity function. The results evaluated to clarify the relationship between crack length, MWCNT filler ratio, and electrical conductivity properties. MWCNTs are generally preferred as the reinforcements for their very high aspect ratio and excellent specific surface area properties. However, the electrical conductivity of the nanocomposites is owing to the constitution of a continuous conductive 3D network of MWCNT and Graphite in the NR matrix.

A novel study for the estimation of crack propagation in concrete using machine learning algorithms

Abstract In this study, the crack pattern and propagation in a random concrete surface has been examined using machine learning algorithm called voronoi diagrams. A random photo of a concrete crack located on the surface is taken from a common source and the crack dimensions and directions have been measured. After then, the crack has been divided into 12 parts to evaluate the machine learning algorithm’s capability for estimating the crack pattern including its direction. Consequently, it has been shown that this novel technique is precise, quick, cheap and useful for monitoring and estimating crack propagation on concrete surfaces. Besides, it has great potential for not only cement and concrete industries and also for many different industries in the means of automation, sustainability, safety, cost and time savings for observing and estimating crack propagations or other properties of materials.

Overlapping Lattice Modeling for concrete fracture simulations using sequentially linear analysis

Modeling concrete fracture is important in order to uncover accurately the sources of distress which lead to the damage or failure of structures. Many different numerical approaches have been used in the past employing either a smeared or a discrete cracking approach. Those models have difficulty in capturing the local nature of cracking, as well as the direction of crack propagation. Lattice modeling and peridynamics (PD) are some of the more recent nonlocal fracture simulation tools which possess advantages, such as ease of modeling and accuracy of crack propagation simulations with few key parameters. In this work, we employ an overlapping lattice approach, where the continuum is discretized using truss elements extending over a predefined horizon similar to the concept used in PD with the sequentially linear analysis technique. Simulation results for several reinforced concrete (RC) and un‐RC tests demonstrate the ability to estimate crack propagation directions and widths accurately, with the proposed modeling approach also offering a rather simple and intuitive approach.

A new method for estimating fatigue life of notched specimen

Fatigue life of engineering structure contains two parts: crack initiation life and crack propagation life. Fracture mechanics is adopted to estimate crack propagation life in the real engineering structures and has made some achievements. Actually, the existing study indicated that fatigue crack initiation is also an important period in the whole fatigue life. So, a new method to predict the whole fatigue life of notch components is proposed based on the theory of damage mechanics in this paper. The damage evolution equation of notch specimen under tension compression loading is obtained based on closed-form solution. The stress distributions of notch root are analyzed by finite element method. The whole fatigue life of notch specimen is estimated by the proposed method when stress concentration factor is different. It has been verified that the results calculated by proposed method is close to the experimental results and the model put forward in this paper is superior to Manson-Coffin Law. The result indicates that the proposed method is concise, effective and feasible for practical application.

Estimation of crack propagation in polymer electrolyte membrane fuel cell under vibration conditions

In transportation applications, the main reasons of mechanical damage in polymer electrolyte membrane fuel cell (PEMFC) are road-induced vibrations and impact loads. The most vulnerable place of these cells is the interface between membrane and catalyst layer in the membrane electrode assembly (MEA). Hence, studies on mechanical strength of PEMFC should focus on that interface. The objective of present study lies in the fact that employing a prediction method to investigate the damage propagation behavior of vibration applied PEMFC using artificial neural network (ANN). The data available in the literature are used to constitute an ANN model. Three-layer model; input, hidden and output, are used for construction of ANN structure. Initial delamination length (a), amplitude (A), frequency (ω) and time (t) are used as input neurons whereas delamination length is output. Levenberg–Marquardt algorithm is selected as learning algorithm. On the other hand, number of hidden layer neuron is decided with the use of different neuron numbers by trial and error method. It is concluded that prediction capability of ANN model is in allowable limits and model can be suggested as efficient way of delamination length estimation.

Crack propagation estimation by deep learning: crack propagation behavior training using s-version finite element method

Crack propagation estimation by deep learning: crack propagation behavior training using s-version finite element method

Fatigue Crack Propagation in Haynes 230: A Comparison between Single and Polycrystal Crack Closure Levels

An experimental campaign was developed to evaluate fatigue crack growth in Haynes 230. The effects of plasticity induced crack closure were investigated with Digital Image Correlation. In particular, crack opening levels were measured with the digital extensometer technique, which allowed the evaluation of crack flanks relative displacements. Experimental results were compared with a reference da/dn – ΔKeff curve and with the data of a previous study, which analyzed single crystal propagation. It was found that the adoption of crack closure local measurements provided an accurate estimation of crack propagation driving forces, since all the experimental points from single crystals and polycrystals collapse onto the da/dn – ΔKeff curve.

Damage analysis of composites reinforced with Alfa fibers: Viscoelastic behavior and debonding at the fiber/matrix interface

ABSTRACTIn this article, we first review state‐of‐the‐art experimental techniques and measurements to characterize the mechanical properties of anisotropic vegetal alfa fibers, epoxy‐resin, and the behavior of the interphase between the matrix and alfa fibers. Second, we conduct experimental tests to determine the mechanical properties of fibers, resin, and the interphase. Third, we carry out a series of finite element simulations to predict damage initiation and to estimate crack propagation in alfa‐fiber/epoxy‐resin (AFER) composites. Different tests to determine the longitudinal Young's modulus of alfa fibers and epoxy resin as well as nanoindentation tests to obtain the transverse stiffness of the fibers are presented. Experimental results from the characterization are introduced in a micromechanical model to estimate, using the concept of the energy release rate (ERR), the matrix crack, and its interaction with interfacial debonding. The wettability problems in the preparation of vegetable composites and their effect on fiber‐matrix interfacial debonding are also addressed. The analysis of the damage behavior of AFER composites demonstrates that under load transverse to the fiber axis, a crack initiated in the matrix is propagated perpendicular to the direction of the load. Near the interface, the ERR decreases and this energy is higher in the presence of interfacial debonding areas generated by problems of fiber wettability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43760.

Characterization of Damage During Low Cycle Fatigue of a 304L Austenitic Stainless Steel as a Function of Environment (Air, PWR Environment) and Surface Finish (Polished, Ground)

304L austenitic stainless steel is notably used to manufacture pipes in primary cooling circuits of nuclear power plants operating at a temperature close to 300°C in a specific aqueous environment. Customarily, pipes are roughly polished, however, after some interventions, a few zones might be ground. Start-ups, shutdowns and operating transients of the reactor produce Low Cycle Fatigue (LCF) loadings with different strain rates. These solicitations and the modified surface finish create specific conditions whose effects must be taken into account. In order to understand if there is a joint influence of the PWR environment and surface roughness on the successive stages of fatigue damage leading to failure, fatigue tests were conducted at 300°C under a total strain amplitude of ± 0.6%. Two environments were used, laboratory air and simulated PWR primary aqueous environment. Two surface finishes were investigated, namely fine mechanical polishing and grinding (Rt of about 40μm). The analysis of the damage process is based on data concerning crack density, crack length and striation spacing. The integration of the relation between the striation spacing and the strain intensity factor ΔKɛ, provides an estimation of crack propagation. It is confirmed that in PWR environment one striation can be considered as the crack advance during one fatigue cycle. Moreover, the specific crack front geometry observed in ground specimens and resulting from successive microcrack coalescences explains the reduction in fatigue life induced by grinding.

Simulating Crack Propagation of a Selected Structural Component of the PZL-130 Orlik TC-II Aircrafts

Abstract This paper presents the process of estimating crack propagation within a selected structural component of the PZL-130 Orlik TC-II using a numerical model. The model is based on technical drawings and measurements of the real structure. The proper definition of the geometry, including the location and size of the gap between elements, is significant for mesh generation. During the simulation process the gap is combined node by node. Each time, the strain energy release rate (G) is calculated. The stress intensity factor and geometry correction factor are defined for consecutive crack lengths, and used further on to estimate crack propagation.

Effect of loading rate on fracture toughness and failure micromechanisms in marble

Fracture experiments in a notched semi-circular bend configuration were conducted to characterize rate effects and failure micromechanisms of a marble using a servo-hydraulic machine and a modified split Hopkinson pressure bar. Three real-time measurement techniques were used to estimate crack propagation velocities and full-field deformation fields. Micro-measurement techniques were employed to qualitatively and quantitatively identify micrograph and surface morphology. Based on the theory of fracture mechanics, a micromechanical model was presented to examine the intergranular and transgranular fracture. The results indicated that fracture toughness and surface roughness were dependent on loading rate, which were induced by the intrinsic failure mechanisms.

Experimental and numerical investigation into effect of elevated temperature on fretting fatigue behavior

t Fretting fatigue damage occurs in contacting parts when they are subjected to fluctuating loadingsand sliding movements at the same time. This phenomenon may occur in many applications such asbearings/ shafts, bolted and riveted connections, steel cables, and steam and gas turbines. In this paper,the effect of elevated temperature on fretting fatigue life of Al7075-T6 is investigated using a new device forfretting fatigue tests with variable crank shaft mechanism. Also a finite element modeling method was usedto estimate crack propagation lifetime in aluminum alloy, Al7075-T6 specimens at elevated temperatureunder fretting condition. In this method, shear and normal stresses that are caused by contact load areupdated at each crack growth increment. Finally, a comparison between the experimental and numericalresults is done in order to evaluate the FE simulation.Department of mechanical engineering, Islamic Azad University, Takestan Branch, Takestan, IranThe experimental results show that: (i) fretting fatigue life of the material increases with temperature up to350°C by 180% for low stresses and decreases by 40% for high stresses, (ii) this fashion of variation offretting fatigue life versus temperature is believed to be due to degradation of material properties whichoccurs by overaging and wear resistance increase due to oxidation of aluminum alloy. While overaginggives rise to degradation of mechanical strength of material and hence the reduction of its fretting fatiguelife, surface oxidation of the specimens brings some improvement of fatigue behavior of the material.Metallurgical examination of the specimens reveals that temperature results in precipitation of impurities ofal-7075-T6. The size of precipitated impurities and their distances gets bigger as temperature increases.This could be a reason for material degradation of specimens which are exposed to heating for longer timeduration.

Effects of Shot‐Peening on Fretting Fatigue Crack Growth Behavior in Ti‐6Al‐4V

Abstract: The effects of shot‐peening on fretting fatigue crack growth behaviour in titanium alloy, Ti‐6A1‐4V were investigated. Three shot‐peening intensities: 4A, 7A and 10A were considered. The analysis involved the fracture mechanics and finite element sub‐modelling technique to estimate crack propagation lives. These computations were supplemented with the experimentally measured total fretting fatigue lives of laboratory specimens to assess the crack initiation lives. Shot‐peening has significant effect on the initiation/propagation phases of fretting fatigue cracks; however this effect depends upon the shot‐peening intensity. The ratio of crack initiation and total life increased while the ratio of the crack propagation and total life decreased with an increase of shot‐peening intensity. Effects of residual compressive stress from shot‐peening on the crack growth behaviour were also investigated. The fretting fatigue crack propagation component of the total life with relaxation increased in comparison to its counterpart without relaxation in each shot‐peened intensity case while the initiation component decreased. Improvement in the fretting fatigue life from the shot‐peening and also with an increase in the shot‐peening intensity appears to be not always due to increase in the crack initiation resistance from shot‐peened induced residual compressive stress.